Filter cartridges of the type to which this invention is addressed are described in U.S. Pat. No. 5,180,489, the contents of which are incorporated by reference therein. Cartridges, such as the ones shown in the '489 patent are commonly used for filtering deionized water used in electrical discharge machines. The rate of water flow and the level of contamination present in the water flow are both high, and it is common to replace filter cartridges used in these applications frequently. The filter cartridge shown in the Figures of the '489 patent has a liquid conducting conduit 22 in fluid communication with an inlet 18 and extending upwardly from the inlet 18 toward an open end 24 adjacent the top end 14 of a housing 12 of the cartridge. The conduit is perforated over substantially all of its length, beginning at the inlet and terminating just short of the open end. The open end is perforated to allow liquid and contaminants contained in the liquid to enter the inner chamber of the filter cartridge. The cartridge includes a pleated filter medium 26 disposed between the inlet and an outlet 20. The filter medium is spaced apart from the conduit 22 to define a space between the conduit and the filter medium 26. The conduit 22 below its open end 24, the filter medium 26 and the bottom end 16 of the filter cartridge together, define a trap for trapping liquid flowing into the housing, so that the liquid may escape the housing through the outlet 20 only by passing through the filter medium 26, thereby preventing backflow through the conduit.
It is a disadvantage of this filter cartridge shown in the '489 patent that the cartridge tends to hold a considerable amount of liquid while it is being changed, and this makes changing the cartridge physically more difficult because the cartridge is heavy, as well as requiring the spent cartridge and liquid contained therein be disposed of, which prevents the cartridge from being crushed, for example, to reduce its size.
It is an object of this invention to provide a filter cartridge of the type generally shown in the '489 patent that allows substantially all of the liquid contained therein to drain quickly from the cartridge being replaced, without contaminating the clean fluid.